The present invention relates to attenuation of noise in gas flowing through tubes, and in particular to attenuation of specific frequency bands of noise. More particularly, the present invention relates to attenuation of specific frequency bands of noise in engine exhaust gas flowing through a tube while minimizing back pressure effects from the noise attenuation system.
Internal combustion engines typically include an exhaust manifold that collects exhaust gas from engine cylinders and channels it into an exhaust pipe or tube. The exhaust gas flowing into the tube carries engine noise. Factors such as engine type and the range of pressures, temperatures, and velocities of the exhaust gas traveling through the tube affect the characteristics of the noise in the gas, such as amplitude and frequency. Exhaust systems include a muffler system designed to reduce the noise in the exhaust gas over the complete range of audible frequencies for a given engine type. A particular engine type can often produce problem noise frequencies that existing muffler systems do not attenuate effectively.
Methods for addressing problem noise frequencies in exhaust gas flowing through a tube include absorption, dispersion, and cancellation. Absorption reduces noise through use of components that convert acoustic energy to some other form, such as heat. Dispersion reduces problem noises by converting the acoustic energy at one frequency or range of frequencies to other frequencies at which there is no or less of a problem. Cancellation reduces problem noises by reflecting acoustic signals or noise so that the reflected signal negates the noise of acoustic signals traveling in opposing directions. A design constraint for all of these methods in reducing problem noises in engine exhaust is the need to minimize the effect of the noise reduction system on back pressure within the exhaust pipe or tube.
Common methods of addressing problem noise frequencies include addition of a resonator or modifications to either the engine or the muffler to reduce the problem noise. Mufflers, which typically include baffles and tuning volumes for noise reduction, are formed as a separate component from the remainder of the exhaust system. Mufflers invariably include a volume outside of the tube carrying the exhaust gas to aid in noise attenuation. Resonators are also formed as a separate component and similarly employ a separate volume outside the tube to attenuate problem noises. Both mufflers and resonators are installed at appropriate points in the exhaust pipe or tube carrying the exhaust gas from the engine to minimize the effect of back pressure created by the muffler or resonator on engine performance.
According to the present invention, a noise attenuation system is provided for use in attenuating noise in gas flowing through an exhaust system. The noise attenuation system includes a tube having a inlet end, an outlet end, and an inner surface defining a passageway through which the exhaust product flows. The noise attenuation system further includes an acoustic reflector attached to the tube. The acoustic reflector includes a tab that extends across the passageway. The tab includes a surface facing generally obliquely toward the inlet end of the tube. The surface is sized and arranged to occlude less than about fifty percent of a cross-sectional area of the passageway that is perpendicular to a longitudinal axis extending through the passageway.
In preferred embodiments, the acoustic reflector is a tab formed from a thin strip of metal and occludes between about thirty percent and about fifty percent of the cross-sectional area of the passageway. The tube includes an inlet and an outlet, and the acoustic reflector can be coupled across the outlet. The tab includes a central region that can be arcuate or V-shaped, with the central region convex facing the inlet and concave facing the outlet. The acoustic reflector in another embodiment includes two tabs arranged in a cross-shaped configuration across the tube outlet. The two tabs are arcuate, convex facing the inlet and concave facing the outlet, and together occlude less than about fifty percent of the cross-sectional area of the passageway.
In other embodiments, a noise attenuation system includes a muffler having a housing and an inlet coupled to a tuning tube within the muffler housing. An acoustic reflector is coupled across the outlet of the tuning tube. In still other embodimens, a noise attenuation system includes a catalytic converter housing having an inlet, and a tube including an acoustic reflector is coupled to the inlet of the catalytic converter housing.
A method of attenuating noise in gas flowing through an exhaust system tube in accordance with the present invention includes the steps of providing a tube including a passageway, an inlet end, and an outlet end, and providing a tab including a first end, a second end, a central region, a first surface, and a second surface. The tab is coupled to the tube so that the tab occludes between less than about fifty percent of the cross-sectional area of the passageway. The step of providing a tab includes providing a tab formed from a thin metal strip. The tube has an edge defining an opening to the passageway, and the step of coupling the tab to the tube includes coupling the first and second ends of the tab to spaced-apart locations on the edge. The step of providing a tab includes providing a tab with a convex surface or V-shaped surface. The step of providing a tube includes providing a tuning tube within a muffler or a manifold tube for coupling to an inlet of a catalytic converter.
Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.